Canadian Journal of Zoology Demography of sooty fox sparrows following a shift from a migratory to resident life history Journal: Canadian Journal of Zoology Manuscript ID cjz-2017-0102.R2 Manuscript Type: Article Date Submitted by the Author: 08-Oct-2017 Complete List of Authors: Visty, Hannah; University of British Columbia, Forest and Conservation Sciences Wilson, Scott; Environment and Climate Change Canada, National Wildlife Research CentreDraft Germain, Ryan; University of British Columbia, Forest and Conservation Science; University of Aberdeen, Institute of Biological and Environmental Sciences Krippel, Jessica; University of British Columbia, Forest and Conservation Science Arcese, Peter; Univ of British Columba, sooty fox sparrow, demography, population growth, MIGRATION < Keyword: Discipline, colonization, Passerella unalaschcensis https://mc06.manuscriptcentral.com/cjz-pubs Page 1 of 20 Canadian Journal of Zoology 1 Demography of sooty fox sparrows following a shift from a migratory to resident life history Hannah Visty1, Scott Wilson2, Ryan Germain1,3, Jessica Krippel1, and Peter Arcese1 1Department of Forest and Conservation Sciences, 2424 Main Mall, Vancouver, BC V6T 1Z4; [email protected]; [email protected]; [email protected] 2Environment and Climate Change Canada, National Wildlife Research Centre, 1125 Colonel by Drive, Ottawa, ON K1A 0H3; [email protected] 3Institute of Biological and Environmental Sciences, Zoology Building, University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ, United Kingdom; [email protected] Draft Contact author: Hannah Visty, Department of Forest and Conservation Sciences, 2424 Main Mall, Vancouver, BC V6T 1Z4; [email protected]; Phone: 778-985-6200; Fax: 8229103 https://mc06.manuscriptcentral.com/cjz-pubs Canadian Journal of Zoology Page 2 of 20 2 Demography of sooty fox sparrows following a shift from a migratory to resident life history Hannah Visty (H. Visty), Scott Wilson (S. Wilson), Ryan Germain (R. Germain), Jessica Krippel (J. Krippel), and Peter Arcese (P. Arcese) Abstract Identifying causes and consequences of variation in species life history has the potential to improve predictions about how climate and land use change may affect the demography and distribution of species in future. Sooty fox sparrows (Passerella unalaschcensis J.F. Gmelin, 1789; or commonly grouped within Passerella iliaca B. Merrem, 1786) were migrants that rarely bred in the Georgia Basin of British Columbia prior to ~1950 but have since established resident populations. Data on 270 color-banded birdsDraft and 54 nests on Mandarte Is., BC, allowed us to estimate demographic vital rates and population growth in one recently established population. Annual fecundity (F), estimated as the product of the number of broods initiated (1.5 ± 0.01; mean ± sd), clutch size (2.82 ± 0.44), and probability of survival to fledging (0.68 ± 0.02), exceeded values reported for migrants, supporting the hypothesis that residents invest more in reproduction on average than migrants within species. Estimating juvenile and adult overwinter survival (Sj = 0.32 ± 0.06, and Sa = 0.69 ± 0.05) next allowed us to simulate an expected distribution of population growth rates as: λexp = Sa + (Sj × F), given parameter error. Our estimate of λexp (1.61 ± 0.57) implies expeditious population growth, consistent with the species’ recent colonization of the region. Keywords: sooty fox sparrow, Passerella unalaschcensis, demography, population growth, migration, colonization https://mc06.manuscriptcentral.com/cjz-pubs Page 3 of 20 Canadian Journal of Zoology 3 Introduction Climate, land cover and species life histories often co-vary (e.g., Hudson and Keatley 2010; Gimona et al. 2015), which suggests that by identifying causal mechanisms we can improve predictions about how environmental change may affect species life histories in future (e.g., Winkler et al. 2002; Visser 2008; Pacifici et al. 2015; Beever et al. 2017). Fox sparrows (Passerella iliaca B. Merrem, 1786) offer an interesting case in point, given the species’ current status as a polytypic, single-brooded migrant (Bendire 1889; Swarth 1920; Threlfall and Blacquiere 1982; Garrett et al. 2000; Weckstein et al. 2002). In contrast, Zink (1994) provided genetic evidence in support of a phylogenetically distinct sooty fox sparrow (Passerella unalaschcensis J.F. Gmelin, 1789; sometimes recognized as a subspecies group within P. iliaca, e.g., Chesser et al. 2016) in coastal regionsDraft of the Pacific Northwest, and Wahl et al. (2005) reported that sooty fox sparrows have become residents of the coastal lowlands and Gulf and San Juan Islands of British Columbia (BC) and Washington State (WA), possibly producing multiple broods annually. We ask in this paper whether these differences in historical and modern accounts of sooty fox sparrows represent a life history shift from a migratory to residential lifestyle, similar to shifts reported in a variety of species as an example of acclimatization to environmental change (e.g., Winkler et al. 2002; Visser 2008; Beever et al. 2017). Historical records prior to ~1950 indicate that sooty fox sparrows were short distance migrants in coastal British Columbia, with only three breeding records from western Vancouver Island (Swarth 1920; Munro and Cowan 1947). By 1983, Guiguet (1983) listed sooty fox sparrows as resident on Vancouver Island, and other sources recognize them as residents of the Southern Gulf and San Juan Islands (Baron and Acorn 1997; Campbell et al. 2001; Wahl et al. 2005). Multiple lines of evidence also indicate that sooty fox sparrows are increasing in this https://mc06.manuscriptcentral.com/cjz-pubs Canadian Journal of Zoology Page 4 of 20 4 region (National Audubon Society 2010; Hearne 2015), as might be expected following successful colonization and the adoption of a residential lifestyle. This expectation arises from well-known trade-offs in migratory and reproductive tactics, which influence species demography, ecology and evolution (Rolshausen et al. 2009; Tökölyi and Barta 2011). Shifts from migratory to residential lifestyles have been linked to increases in reproductive effort (Gillis et al. 2008; Bruderer and Salewski 2009). Comparative studies of birds also showed that short- distant migrant birds bred longer and initiated more broods with smaller clutches than long distance migrants of the same species (Sandercock and Jaramillo 2002). In this paper we estimate demographic vital rates and population growth in a resident, individually-marked population of sooty fox sparrows that colonized Mandarte Island, BC, in 1975. Based on the studies above, we expectedDraft to observe that the sooty fox sparrows we studied would have longer breeding seasons, initiate more nests annually, and lay smaller clutches than observed in migratory fox sparrows. In the absence of commensurate reductions in survival (e.g., Sandercock and Jaramillo 2002), we also expected to observe evidence of positive population growth. Methods We studied sooty fox sparrows on Mandarte Is. (c. 6 ha), located ~11km south of Victoria International Airport in southwestern BC, Canada, also the site of a long-term study of song sparrows (Melospiza melodia; 1960-63 and 1975-2017, Tompa 1963; Arcese et al. 1992; Smith et al. 2006). Sooty fox sparrows colonized Mandarte Is. in 1975 and became the most common passerine on the island ~2010 (Tompa 1963; Drent et al. 1964; Johnson 2015). We began collecting demographic data on sooty fox sparrows opportunistically in 2010 while also monitoring song sparrows. Observations typically spanned March – August annually, including https://mc06.manuscriptcentral.com/cjz-pubs Page 5 of 20 Canadian Journal of Zoology 5 5-20 days per year of netting and census during overwinter trips in 2012 – 14, and up to 60 days per winter from 1982 – 1987, indicating that most or all sooty fox sparrows observed on the island were resident year-round. From 2010 – 2016, 123 nestling, 82 juvenile, and 65 adult sooty fox sparrows were fitted with a numbered metal and 1-3 coloured plastic bands to facilitate re- sighting. A smaller number of distinctly marked fox sparrows (1989; or ‘naturally’ identifiable by a unique distribution of white feathers from 1982 – 1987) originally confirmed year-round residence in this population, but were not observed in sufficient detail to use in analyses presented here. We thus used birds marked from 2010 – 2016 to estimate juvenile annual survival (Sj) and adult annual survival (Sa) using recapture and re-sighting data and program MARK (version 8.x). When doing so, individuals bandedDraft outside the formal re-sighting period (May 1 –June 30) in year t to t+1 were entered into the survival encounter history as if they were observed in the re-sighting period in year t+1. ‘Juveniles’ include birds banded as nestlings (~4-8 days-old), fledglings (~12-24 days-old), or independent young (<76 days-old). Our initial analyses indicated no difference in overwinter survival estimates whether nestlings and older young were treated separately or pooled; we therefore pooled these groups to increase sample size and simplify our population model by estimating survival for single period (nestling to recruit: ‘juvenile survival’). Candidate models were developed using combinations of the most common determinants of survival (age in two classes: juvenile or adult, variation by year of observation, or simply held constant); the ‘logit’ link function was used to test all models. Model goodness-